Anti-friction bearing

ABSTRACT

An anti-friction bearing is made by replacing one or more of the conventional roller elements with TFE or FEP elements of the same size and shape. After a short break-in period, a thin antifriction film or TFE or FEP will transfer onto the races and the other bearing elements and will be maintained throughout the life of the bearing by additional transfer from the fluoroplastic roller elements to preclude the surface coating from wearing through.

D United States Patent [1 1 [111 3,764,188 Suska [4 1 Oct. 9, 1973ANTI-FRICTION BEARING [75] Inventor: Charles R. Suska, Roxbury, Conn.Pmfmry Exam" 'er Char1eS Myhre ASSZSIGH! Exammer-Frank Susko Assignee!The Stanley Works, New Britain, AttorneyGranville M. Brumbaugh et a1.

Conn.

22 Filed: Nov. 19, 1971 [571 ABSTRACT An anti-friction bearing is madeby replacing one or [21] Appl' more of the conventional roller elementswith TFE or FEP elements of the same size and shape. After a [52] [1.8.CI. 308/187 ho re k-in p rio a h n iri ion film or TFE [51] Int. Cl.Fl6c 33/66 r FEP will transfer onto the races and the other bear- [58]Field of Search 308/.007, 188, 187 ing elements and will be maintainedthroughout the life of the bearing by additional transfer from the [56]References Cited fluoroplastic roller elements to preclude the surfaceFOREIGN PATENTS OR APPLICATIONS I France 308/.007

coating from wearing through.

2 Claims, 1 Drawing Figure PATENTEU BET 91975 CHARLES R. susKA vANTI-FRICTION BEARING BACKGROUND OF THE INVENTION This invention relatesto an improved low-friction bearing and, more particularly, to a methodand appalast as long as the apparatus in which his installed and wouldrequire no maintenance whatsoever. It would be inexpensive to produce,and amenable to high-volume production. It would offer the sameload-bearing capacity as present conventional bearings without anincrease in size, and would provide quiet, friction-free operation for amuch longer life.

Until now, the ideal bearing has never been ap proached. However, amongthe various attempts in the past to achieve the ideal bearing, theclosest approximation has been the sealed bearing. A sealed bearing isone which is manufactured, lubricated, and sealed at the factory so thatit need never be lubricated or otherwise maintained again.

Bearings are essentially of two varieties; the first is a conventionalbearing using greases or oils having various additives designed toreduce the rate of lubricant deterioration and migration from thebearing. While these bearings are generally longer wearing and moretrouble free than conventional bearings, their life is limited by thelife of the lubricant. Eventually each known grease will dry, oxidize orotherwise deteriorate, or become contaminated, leaving thebearing'without the proper quality of lubrication, and consequently with ashortened remaining life; or the lubricant may be washed out of thebearing causing premature failure.

The second variety of bearing is the TFE (polytetrafluoroethylene)coated bearing. TFE coated bearings have a thin layer of TFE on thebearing element or the raceways, or both, to provide low-frictioncontact therebetween. Initially, these bearings provide excellentperformance and do not depend on the transitory life of conventionallubricants for their continued performance. They have not been widelyaccepted by the art, however, mainly because they areexpensive tomanufacture. In addition, the thin TFE coating eventually wears away andthe resulting steel-to-steel contact swiftly destroys the bearing.

To' correct this problem, it has been proposed to fabricate the rollerelements of solid TFE; While this solution avoids the problem of wearingthrough of the TFE I coating, the poor mechanical strength of the TFEroller elements drastically lowers the mechanical strength of thebearing.

The prior art, therefore, has yet to provide a bearing which approachesthe requirements of the ideal bearing, namely low cost, ease ofproduction, compact size, high compressive strength, long and quietlife,and no need for lubrication.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto pro-v vide a new and improved low-friction long-life bearing ofrelatively small size and strength, and which requires no maintenance.

.Another object of the. present invention is to provide a low-frictionbearing which is as easy and inexpensive to produce and has the'same.size and practically the DESCRIPTION OF THE DRAWINGS A more completeappreciation of this invention and other of its many attendantadvantages will develop as it becomes better understood by reference tothe following detailed description of an illustrative embodiment whenread in connection with the accompanying drawing which shows anelevation, partly in section, of a conventional ball bearing in whichtwo of its conven-' tional steel balls have been replaced with twoTeflon balls of the identical shape and size.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, aball bearing is shown having a conventional pair of raceways l0 and 12separated by a plurality of roller element such as ball bearings 14formed of conventional high strength bearing material such as steel.Naturally, it will be understood that the invention, defined in theappended claims, is generally applicable to ball bearings, rollerbearings,

' and needle bearings as well as any other type of bearings usingrolling elements either existing at present or to be developed in thefuture. While it is considered desirable to seal, this bearing toprevent entrance of abrasive foreign matter, it is not necessary to doso and more economical construction may be achieved for use in cleanenvironments without sealing the bearing.

A TFE or PE? coating on the raceways and roller elements is establishedby replacing two of the conventional roller elements 14 with a likenumber of freely movable fluoroplastic elements 16 of identical size andshape as the original roller elements 14. One or two balls of TFE andPE? is preferable but a greater number of roller elements 14 could bereplaced, according to the contemplated use, but in no event should morethan one-third of the balls be replaced in order to retain the loadcarrying capacity of the bearing. If more than oneroller element 16 isused, they should preferably be spaced at uniform distances in theraceway.

It is necessary that the fluoroplastic elements 16 be freely movable,that is, free to move with the other roller elements around theraceways. This free movement may be achieved within a cage, provided thecage is free, to rotate relative to the raceways. Free movement isdesirable for uniform transference and maintenance of the fluoroplasticcoating, as explained hereinafter.

While solid TFE or FEP is used in the above described embodiment, it isalso possible to fabricate the transferable low-friction materialfluoroplastic elements 16 with a center core or some other materialsurrounded by fluoroplastic material or with a matrix of filaments orsome other material extending therethrough for purposes of strength,durability, or manufacturing convenience. It is only necessary thatthere be a sufficient reservoir of fluoroplastic to establish andmaintain the coating.

More specficially, the transferable low-friction material elements 16may be solid TFE or FEP, or TFE or FEP with a center core of anothermaterial. The transferable low-friction material elements 16 may also beformed of materials such as delrin AF, a product of Du Pont that isformed of about one-fifth TFE fibers ancl the balance acetal, and Fulton404, a product of Liquid Nitrogen Products that is formed of aboutone-fifth TFE granules and the balance acetal. A still further materialfor the elements 16 is Gylon Lubetal Resin, a product of Garlock that isformed of fibrous flake TFE and an acetal resin.

The following theoretical explanation of the mecha nism by which theinvention is though to function is offered for the sake of clarificationby explication of the disclosure rather than limitation in interpretingthe claims appended hereafter.

Although the wear mechanism of fiuoroplastics is not fully understood,it is generally thought that adhesion and the freeing of transferredwear fragments are of major importance. It is known that when TFE isrubbed against other materials a transfer takes place. It is be lievedthat this wear process involves the laying down and then the removal ofthe transferred layers. When the-metal part which has a reasonablysmooth surface, e.g.,' 8 micro-inches, runs against a TFE part, themetal part acquires a coating of TF E so that the working interface isbetween TFE and TFE. As TFE particles wear off of the TFE part, theytransfer to the metal part thereby maintaining the continuity of thefilm, provided the smoothness of the metal surface is within a suitablerange. If the metal part is too rough, it would act as a rasp to rapidlyremove TFE; if the metal part is too smooth, some investigators doubtthat the transference occurs, but there is no general agreement on thispoint. In a ball-bearing application, commercially available balls mightbe too smooth for good transference, but as the raceways need not havethe same finish as the balls it would be an improvement if thetransferred film occurs primarily on the raceways. In other words, itshould be better for transferred film to deposit on both the balls andthe raceways, but if the balls are too smooth to cause good deposits,there would still be a lubricating film separating the metal balls fromthe metal raceways if the deposit can occur on the raceways.

The transference of TFE to the metal surface appears to beself-limiting, that is, once the TFE film hasbeen established on themetal surfaces there'is no further deposition, so the film does notbecome so thick as to interfere with the free movement of the bearingelements within the bearing. This phenomenon is probably due to an equalrate of transfer or wear fragments between TFE surfaces of the TFE partand the coated metal surfaces once the TFE film has been established.The system is therefore inherently economical in its use of the rialsare graphite, molybdeum disulphide, lead oxide,

etc. A surface coating of these materials on the rolling elements andraceways improves bearing life when the oil or grease lubricantis nolonger present, but the improvement would not be as great as for TFE andF EP.

Among the polymer materials, chlorotrifluoroethylene will function inthe same manner as TFE and FEP. The particular characteristics desiredin the low-friction material are good transference to the raceways andother balls, and low-friction characteristics between the surfaces socoated. It is expected that other materials will be developed in thefuture which will function similarly, and it is expressly contemplatedthat as'improved materials are developed they may be substituted for theTFE, FE? and chlorotrifluoroethylene, used in the illustrated example.Accordingly, any material that exhibits low-friction and goodtransference characteristics, hereinafter referred to as transferablelow-friction material, can be used.

By replacing only one or two of the roller elements with freely movableroller elements formed of transferable low-friction material, the loadbearing characteristics of the bearing are changed only slightly. Thesize and complexity of the bearing have not been increased at all andthe manufacturing cost has not been significantly increased, but thewearing characteristics have been improved dramatically. By making thereplacing elements 16 freely movable, the process of transference of thefluoroplastic film is greatly facilitated be cause the elements .16 arefree to contact all bearing surfaces very early in the life of thebearing. Moreover, TFE or FEP is not wasted since only the bearingsurfaces become coated, and after they are coated, transference of thefluoroplastic is sharply reduced.

In construction, the bearing is commonly assembled andlubricated withgrease and then sealed. During this break-in period, that is, while thetransferable lowfriction material is being transferred from the rollerelements 16 to the other roller elements and the raceways, the greeseprovides the customary good lubrication. By the time the grease hasmigrated from the bearing or dried or oxidized, the low-friction surfacehas already been established by transference in ,the presence of thelubricant and is ready to assume its lubricating function. As timepasses, heavy use tends to wear down the low-friction surface layer.However, it is continually being replaced by the reservoir oftransferable lowfriction material which constitutes the replacing rollerelements 16. The low-friction surface will thus last virtuallyindefinitely.

The illustrated embodiment interposes elements 16 between elements 14 sothat elements 16 at all times occupy portions of that circumferencebetween the raceways defined by the locus of points where the elements14 contact each other. In this way, it is assured that there will begood transference of fiuoroplastic from elements 16 to elements 14 andboth raceways.

,Obviously, numerous variations and modifications of -the abovedescribed preferred embodiment or illustrafrom there will retransfer toother rollerelements v and raceway surfaces so that all roller elementsand raceway surfaces may be coated with the transferable low-frictionmaterial and a high number of roller elements of conventional highstrength bearing material may be maintained for high bearing strength.

'2. The bearing defined in claim 1, wherein all of said roller elementsare of substantially the same size and shape, and said transferablelow-friction material is selected from the group consisting ofpolytetrafluoroethylene, fluorinated ethylene propylene andchlorotrifluoroethy'lene. I

1. A bearing, comprising: a pair of raceways having a surface smoothnessof approximately eight micro-inches; at least five freely movable rollerelements disposed between and separating said raceways; at least one butfewer than one-third of said roller elements being uniformly spacedaround said raceways and formed of transferable low-friction material;the other of said roller elements being formed of conventional highstrength bearing material; wherein the roller elements immediatelyadjacent each transferable low-friction material element are formed ofconventional high strength bearing material; whereby the transferablelow-friction material will transfer from the roller element formedthereof to adjacent roller elements and raceway surfaces, and from therewill retransfer to other roller elements and raceway surfaces so thatall roller elements and raceway surfaces may be coated with thetransferable low-friction material and a high number of roller elementsof conventional high strength bearing material may be maintained forhigh bearing strength.
 2. The bearing defined in claim 1, wherein all ofsaid roller elements are of substantially the same size and shape, andsaid transferable low-friction material is selected from the groupconsisting of polytetrafluoroethylene, fluorinated ethylene propyleneand chlorotrifluoroethylene.